1. Field of the Invention
The invention relates to an image scanner, and more particularly, to a flatbed scanner with top and bottom light sources and a moveable light shield for scanning transparent and opaque documents.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a perspective view of a prior art scanner 10. The scanner 10 comprises a housing 12 with a transparent platform 14 on its top end for placing a document to be scanned, and a scanning module (not shown) movably installed under the transparent platform 14 for scanning the document placed on the transparent platform 14. The scanning module usually comprises a light source for emitting light upward and an image converter such as a CCD (charge coupled device) for converting a document image reflected from the document into a digital image. Since the light source is installed under the transparent platform 14, the scanner 10 can only be used to scan opaque documents. If a user needs to scan a transparent document such as a photographic negative film, the user has to place a portable light panel 16 above the transparent platform 14 for emitting light downward through the transparent document and turn off the light source under the transparent platform 14. The portable light panel 16 requires an external power adapter which should be plugged into a power socket before using. Using such a portable light panel 16 is very inconvenient.
Except for the portable light panel 16, many scanner manufacturers provide a removable top cover equipped with a light panel for scanning transparent documents. When scanning a transparent document, a user has to remove the original top cover from a scanner, and install the top cover with the light panel. Because the top cover with the light panel is quite heavy and comprises an electric plug, the replacement of the top cover is also very inconvenient. Besides, if a user frequently needs to scan both transparent and opaque documents, the two top covers of the scanner have to be swapped quite frequently and this is very bothering.